Power control using distortion measurement

ABSTRACT

Apparatus having corresponding methods and non-transitory computer-readable media comprise: a transmitter configured to transmit a signal according to a gain setting, wherein the signal represents a first digital signal; a receiver configured to receive the signal transmitted by the transmitter, and produce a second digital signal based on the signal received by the receiver; a measurement module configured to produce a digital indication of a linearity of the transmitter based on the second digital signal; and a gain setting module configured to control the gain setting in accordance with the digital indication of the linearity of the transmitter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/365,239, entitled “Transmit Power Control UsingDistortion Measurement,” filed on Jul. 16, 2010, the disclosure thereofincorporated by reference herein in its entirety.

FIELD

The present disclosure relates generally to the field of electronic datacommunication. More particularly, the present disclosure relates tocontrolling the transmitted power level of a signal representing digitaldata.

BACKGROUND

The performance of a transmitter depends upon the transmitted powerlevel. As the transmitted power increases beyond a certain level,distortion degrades the transmitted signal. This distortion results indata loss, high bit error rates, and the like. To prevent these effects,power control schemes have been developed.

Two common power control schemes are open loop power control and closedloop power control. In both schemes the goal is to maintain a targetoutput power level at the transmitter. However, both schemes havedrawbacks. In either scheme, any known power level error must besubtracted from the target power level to avoid exceeding specifiedmaximum power levels. This can result in unnecessarily low transmittedpower levels. Furthermore, other factors such as temperature, voltagestanding wave ratio (VSWR), and the like can cause large errors,especially for open loop power control schemes.

To directly address the distortion problem, pre-distortion schemes havebeen developed. According to these schemes, the distortion produced bythe transmitter is measured, and then applied inversely to the sourcesignal, before feeding the source signal to the transmitter. Both analogand digital pre-distortion schemes have been developed. FIG. 1 shows aconventional digital pre-distortion scheme.

Referring to FIG. 1, a digital signal source 102 produces a digitalsignal 104. A digital pre-distortion (DPD) module 106 pre-distortsdigital signal 104 based on DPD information 108 provided by DPD trainingmodule 110. A digital-to-analog converter (DAC) 112 convertspre-distorted digital signal 114 to an analog signal 116. Transmitter118 transmits a signal 120 that represents analog signal 116.Transmitter 118 transmits signal 120 at a power level specified by again setting 122 provided by a gain setting module 124. A receiver 126receives signal 120 and produces a second analog signal 128 based onsignal 120. An analog-to-digital converter (ADC) 130 converts secondanalog signal 128 to a second digital signal 132. DPD training module110 produces DPD information 108 based on a comparison of digitalsignals 104 and 132.

SUMMARY

In general, in one aspect, an embodiment features an apparatuscomprising: a transmitter configured to transmit a signal according to again setting, wherein the signal represents a first digital signal; areceiver configured to receive the signal transmitted by thetransmitter, and produce a second digital signal based on the signalreceived by the receiver; a measurement module configured to produce adigital indication of a linearity of the transmitter based on the seconddigital signal; and a gain setting module configured to control the gainsetting in accordance with the digital indication of the linearity ofthe transmitter.

Embodiments of the apparatus can include one or more of the followingfeatures. In some embodiments, the digital indication of the linearityof the transmitter comprises at least one of digital pre-distortioninformation; an error vector magnitude of the signal received by thereceiver; and a spectral mask of the signal received by the receiver. Insome embodiments, the measurement module comprises: an error vectormagnitude detector configured to measure the error vector magnitude. Insome embodiments, the measurement module comprises: a spectral maskdetector configured to measure the spectral mask. In some embodiments,the gain setting module is further configured to control the gainsetting based on at least one of a measured power level of the signalreceived by the receiver, a voltage of a power supply of the apparatus,and a temperature of the apparatus. In some embodiments, the measurementmodule comprises: a power detector configured to measure the powerlevel. In some embodiments, the measurement module comprises: a voltagedetector configured to measure the voltage of the power supply. In someembodiments, the measurement module comprises: a temperature detectorconfigured to measure the temperature. Some embodiments comprise adigital pre-distortion module configured to produce the first digitalsignal based on a third digital signal and digital pre-distortioninformation; wherein the digital indication of the linearity of thetransmitter comprises the digital pre-distortion information; andwherein the measurement module includes a digital pre-distortiontraining module configured to produce the digital pre-distortioninformation based on the third digital signal and the second digitalsignal. Some embodiments comprise a digital signal source configured toprovide the third digital signal. In some embodiments, the digitalpre-distortion module comprises: a digital filter configured to producethe first digital signal based on the third digital signal and apolynomial; wherein the digital pre-distortion information specifiesvalues for coefficients of the polynomial; and wherein the gain settingmodule is further configured to set the gain setting to a maximum valuethat keeps the values of the coefficient within predetermined ranges. Insome embodiments, the digital pre-distortion information representsdifferences between corresponding samples of the second digital signaland the third digital signal. Some embodiments comprise a communicationdevice comprising the apparatus.

In general, in one aspect, an embodiment features a method comprising:transmitting a signal, from a transmitter, according to a gain setting,wherein the signal represents a first digital signal; receiving thetransmitted signal; producing a second digital signal based on thereceived signal; producing a digital indication of a linearity of thetransmitter based on the second digital signal; and controlling the gainsetting in accordance with the digital indication of the linearity ofthe transmitter.

Embodiments of the method can include one or more of the followingfeatures. In some embodiments, the digital indication of the linearityof the transmitter comprises at least one of digital pre-distortioninformation; an error vector magnitude; and a spectral mask. Someembodiments comprise controlling the gain setting based on at least oneof a measured power level of the signal received by the receiver, avoltage of a power supply of an apparatus comprising the transmitter,and a temperature of the apparatus. Some embodiments comprise producingthe first digital signal based on a third digital signal and digitalpre-distortion information, wherein the digital indication of thelinearity of the transmitter comprises the digital pre-distortioninformation; and producing the digital pre-distortion information basedon the third digital signal and the second digital signal. Someembodiments comprise producing the first digital signal based on thethird digital signal and a polynomial, wherein the digitalpre-distortion information specifies values for coefficients of thepolynomial; and setting the gain setting to a maximum value that keepsthe values of the coefficient within predetermined ranges. In someembodiments, the digital pre-distortion information representsdifferences between corresponding samples of the second digital signaland the third digital signal.

In general, in one aspect, an embodiment features non-transitorycomputer-readable media embodying instructions executable by a computerto perform functions comprising: controlling a gain setting of atransmitter of a signal in accordance with a digital indication of alinearity of the transmitter; wherein the signal represents a firstdigital signal; wherein the digital indication of the linearity of thetransmitter is based on a second digital signal; and wherein the seconddigital signal is based on the signal.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a conventional digital pre-distortion scheme.

FIG. 2 shows elements of a communication device according to anembodiment where transmitter gain is controlled according to digitalindications of the linearity of the transmitter.

FIG. 3 shows a process for the communication device of FIG. 2 accordingto one embodiment.

FIG. 4 shows elements of a communication device according to anembodiment where transmitter gain is controlled according to digitalpre-distortion information.

FIG. 5 shows elements of a communication device according to anembodiment where transmitter gain is controlled according to digitalpre-distortion information and other factors.

FIG. 6 shows elements of a communication device according to anembodiment where transmitter gain is controlled by a processor accordingto digital pre-distortion information and other factors.

FIG. 7 shows elements of a communication device according to anembodiment where transmitter gain is controlled according tomeasurements of error vector magnitudes and/or spectral masks.

The leading digit(s) of each reference numeral used in thisspecification indicates the number of the drawing in which the referencenumeral first appears.

DETAILED DESCRIPTION

Embodiments of the present disclosure provide transmit power controlusing distortion measurement. In particular, various embodiments obtaindigital indications of the linearity of the transmitter, and control thegain of the transmitter based on those indications. Linearity describesthe extent to which the output of the transmitter is proportional to theinput. The digital indications of linearity can include digitalpre-distortion information, error vector magnitudes, spectral masks, andthe like.

FIG. 2 shows elements of a communication device 200 according to anembodiment where transmitter gain is controlled according to digitalindications of the linearity of the transmitter. Although in thedescribed embodiments the elements of communication device 200 arepresented in one arrangement, other embodiments may feature otherarrangements. For example, elements of communication device 200 can beimplemented in hardware, software, or combinations thereof. Furthermore,communication device 200 can communicate wirelessly or over wireline,optical cable or the like.

Referring to FIG. 2, communication device 200 includes a digital signalsource 202, a digital-to-analog converter (DAC) 212, a transmitter 218,a gain setting module 224, a receiver 226, an analog-to-digitalconverter (ADC) 230, and a measurement module 210.

Digital signal source 202 produces a digital signal 204. Digital signal204 can represent any sort of data. DAC 212 converts digital signal 204to an analog signal 216. Transmitter 218 transmits a signal 220 thatrepresents analog signal 216. For example, signal 220 can be aradio-frequency signal or the like. Transmitter 218 transmits signal 220at a power level specified by a gain setting 222 provided by gainsetting module 224. Receiver 226 produces a second analog signal 228based on signal 220. ADC 230 converts second analog signal 228 to asecond digital signal 232. Measurement module 210 produces a digitalindication 208 of the linearity of transmitter 218 based on digitalsignal 232. Digital indication 208 can include digital pre-distortioninformation, error vector magnitudes, spectral masks, and the like.Digital predistortion information describes how the digital signal 204to be transmitted should be pre-distorted to compensate for thedistortion caused by the transmitter 218. An error vector magnitude is ameasure of the difference between the constellation points of thedigital signal 204 to be transmitted and the ideal constellation pointsfor the transmitter. A spectral mask describes the spectrum of thetransmitted signal 220, and can be compared to an ideal spectral mask toobtain a measure of the distortion of the transmitter 218.

In contrast to existing power control schemes, gain setting module 224controls gain setting 222 in accordance with digital indication 208. Insome embodiments, gain setting module 224 controls gain setting 222 inaccordance with other factors in addition to digital indication 208.These factors can include a measured power level of signal 220 receivedby receiver 226, a voltage of a power supply of communication device200, a temperature of communication device 200, and the like.

FIG. 3 shows a process 300 for communication device 200 of FIG. 2according to one embodiment. Although in the described embodiments theelements of process 300 are presented in one arrangement, otherembodiments may feature other arrangements. For example, in variousembodiments, some or all of the elements of process 300 can be executedin a different order, concurrently, and the like.

Referring to FIG. 3, at 302 transmitter 218 transmits signal 220according to gain setting 222. Signal 220 represents digital signal 204.At 304, receiver 226 receives signal 220. At 306, ADC 230 producesdigital signal 232 based on signal 220. At 308, measurement module 210produces digital indication 208 of the linearity of transmitter 218based on digital signal 232. At 310, gain setting module 224 controlsgain setting 222 in accordance with digital indication 208 of thelinearity of transmitter 218.

FIG. 4 shows elements of a communication device 400 according to anembodiment where transmitter gain is controlled according to digitalpre-distortion information. Although in the described embodiments theelements of communication device 400 are presented in one arrangement,other embodiments may feature other arrangements. For example, elementsof communication device 400 can be implemented in hardware, software, orcombinations thereof. Furthermore, communication device 400 cancommunicate wirelessly or over wireline, optical cable or the like.

Referring to FIG. 4, communication device 400 includes a digital signalsource 402, a digital pre-distortion (DPD) module 406, adigital-to-analog converter (DAC) 412, a transmitter 418, a gain settingmodule 424, a receiver 426, an analog-to-digital converter (ADC) 430,and measurement module 210. In communication device 400, measurementmodule 210 includes a DPD training module 410, and the digitalindication of linearity 208 produced by measurement module 210 includesDPD information 408.

Digital signal source 402 produces a digital signal 404. Digital signal404 can represent any sort of data. DPD module 406 pre-distorts digitalsignal 404 based on DPD information 408 provided by DPD training module410. DAC 412 converts pre-distorted digital signal 414 to an analogsignal 416. Transmitter 418 transmits a signal 420 that representsanalog signal 416. For example, signal 420 can be a radio-frequencysignal or the like. Transmitter 418 transmits signal 420 at a powerlevel specified by a gain setting 422 provided by gain setting module424. Receiver 426 produces a second analog signal 428 based on signal420. ADC 430 converts second analog signal 428 to a second digitalsignal 432. DPD training module 410 produces DPD information 408 basedon a comparison of digital signals 402 and 432.

In contrast to existing power control schemes, gain setting module 424generates gain setting 422 based on DPD information 408. In someembodiments, DPD module 406 includes a digital filter configured toproduce digital signal 414 based on digital signal 404 and a polynomial.In such embodiments, DPD information 408 specifies values forcoefficients of the polynomial, and gain setting module 424 generatesgain setting 422 based on the values of those coefficients. For example,gain setting module 424 can set gain setting 422 to the maximum valuethat keeps the coefficient values within predetermined ranges. Asanother example, gain setting module 424 can implement a cost functionor the like to produce a single value based on the coefficient values,and can set gain setting 422 to the maximum value that keeps that valuewithin a predetermined range. In some embodiments, DPD information 408represents differences between corresponding samples of digital signal414 and digital signal 404. In such embodiments, gain setting module 424can set gain setting 422 to the maximum value that keeps the differenceswithin a predetermined range. In some embodiments, DPD information 408is conveyed in other ways. In various embodiments, gain setting module424 can set gain setting 422 using an iterative approach, or in oneshot.

FIG. 5 shows elements of a communication device 500 according to anembodiment where transmitter gain is controlled according to digitalpre-distortion information and other factors. Although in the describedembodiments the elements of communication device 500 are presented inone arrangement, other embodiments may feature other arrangements. Forexample, elements of communication device 500 can be implemented inhardware, software, or combinations thereof. Furthermore, communicationdevice 500 can communicate wirelessly or over wireline, optical cable orthe like.

Referring to FIG. 5, communication device 500 includes a gain settingmodule 524, measurement module 210 includes DPD training module 410, apower detector 534 and other detectors 536, and the digital indicationof linearity 208 produced by measurement module 210 includes DPDinformation 408, a power level indication 538, and indications 540 ofother measurements. The remaining elements of communication device 500are described above with reference to FIG. 4. Referring again to FIG. 5,power detector 534 measures a power level of signal 420 received byreceiver 426, and provides an indication 538 of the power level to gainsetting module 524. Other detectors 536 measure other factors, such as avoltage of a power supply of communication device 500, a temperature ofcommunication device 500, and the like, and provide indications 540 ofthese measurements to gain setting module 524. Gain setting module 524generates gain setting 422 based on DPD information 408 and indications538 and 540. Gain setting module 524 can use the indication 538 of thepower level to implement maximum and/or minimum power levels. A maximumpower level can be set, for example, to comply with FCC restrictions. Aminimum power level can be set, for example, to try a differentmodulation scheme/data rate when the power level goes below the minimumlevel. Indications 540 can also be used to adjust the output powerlevel, for example to allow for ongoing gain adjustments between DPDtraining sessions. For example the gain can be changed in response to atemperature change, according to a known relationship betweentemperature and gain, to maintain a constant power level.

FIG. 6 shows elements of a communication device 600 according to anembodiment where transmitter gain is controlled by a processor accordingto digital pre-distortion information and other factors. Although in thedescribed embodiments the elements of communication device 600 arepresented in one arrangement, other embodiments may feature otherarrangements. For example, elements of communication device 600 can beimplemented in hardware, software, or combinations thereof. Furthermore,communication device 600 can communicate wirelessly or over wireline,optical cable or the like.

Referring to FIG. 6, communication device 600 includes a gain settingmodule 624; measurement module 210 includes DPD training module 410,power detector 534, other detectors 536, and a processor 602; and thedigital indication of linearity 208 produced by measurement module 210includes a gain control signal 604 that is based on DPD information 408,a power level indication 538, and indications 540 of other measurements.The remaining elements of communication device 600 are described abovewith reference to FIGS. 4 and 5. Referring again to FIG. 6, DPD trainingmodule 410 provides DPD information 408 to processor 602. Power detector534 measures a power level of signal 420 received by receiver 426, andprovides an indication 538 of the power level to processor 602. Otherdetectors 536 measure other factors, such as a voltage of a power supplyof communication device 600, a temperature of communication device 600,and the like, and provide indications 540 of these measurements toprocessor 602. Processor 602 provides a gain control signal 604 to gainsetting module 524 based on DPD information 408 and indications 538 and540. Gain setting module 524 generates gain setting 422 based on gaincontrol signal 604. Processor 602 performs calculations based on basedon DPD information 408 and indications 538 and 540, while gain settingmodule 624 provides a hardware interface between processor 602 andtransmitter 418.

FIG. 7 shows elements of a communication device 700 according to anembodiment where transmitter gain is controlled according tomeasurements of error vector magnitudes and/or spectral masks. Althoughin the described embodiments the elements of communication device 700are presented in one arrangement, other embodiments may feature otherarrangements. For example, elements of communication device 700 can beimplemented in hardware, software, or combinations thereof. Furthermore,communication device 700 can communicate wirelessly or over wireline,optical cable or the like.

Referring to FIG. 7, communication device 700 includes a gain settingmodule 724; measurement module 210 includes power detector 534, otherdetectors 536, and an error vector magnitude/spectral mask (EVM/SM)detector 702; and the digital indication of linearity 208 produced bymeasurement module 210 includes power level indication 538, indications540 of other measurements, and EVM/SM measurements 708. The remainingelements of communication device 700 are described above with referenceto FIGS. 4 and 5. Referring again to FIG. 7, EVM/SM detector 702measures an error vector magnitude and/or spectral mask of signal 420received by receiver 426, and provides an indication 708 of themeasurements to gain setting module 724. Gain setting module 724generates gain setting 422 based on indication 708 and indications 538and 540. For example, gain setting module 724 can set gain setting 422to the maximum gain that keeps the EVM and/or spectral mask withinpredetermined requirements. Gain setting in this manner can beimplemented using an iterative or one-shot approach, and can be combinedwith indications 538 and 540 to limit the maximum and/or minimumtransmitter power. Indications 540 can be used to adjust thosemaximum/minimum values.

Various embodiments of the present disclosure can be implemented indigital electronic circuitry, or in computer hardware, firmware,software, or in combinations thereof. Embodiments of the presentdisclosure can be implemented in a computer program product tangiblyembodied in a computer-readable storage device for execution by aprogrammable processor. The described processes can be performed by aprogrammable processor executing a program of instructions to performfunctions by operating on input data and generating output. Embodimentsof the present disclosure can be implemented in one or more computerprograms that are executable on a programmable system including at leastone programmable processor coupled to receive data and instructionsfrom, and to transmit data and instructions to, a data storage system,at least one input device, and at least one output device. Each computerprogram can be implemented in a high-level procedural or object-orientedprogramming language, or in assembly or machine language if desired; andin any case, the language can be a compiled or interpreted language.Suitable processors include, by way of example, both general and specialpurpose microprocessors. Generally, processors receive instructions anddata from a read-only memory and/or a random access memory. Generally, acomputer includes one or more mass storage devices for storing datafiles. Such devices include magnetic disks, such as internal hard disksand removable disks, magneto-optical disks; optical disks, andsolid-state disks. Storage devices suitable for tangibly embodyingcomputer program instructions and data include all forms of non-volatilememory, including by way of example semiconductor memory devices, suchas EPROM, EEPROM, and flash memory devices; magnetic disks such asinternal hard disks and removable disks; magneto-optical disks; andCD-ROM disks. Any of the foregoing can be supplemented by, orincorporated in, ASICs (application-specific integrated circuits).

A number of implementations have been described. Nevertheless, variousmodifications may be made without departing from the scope of thedisclosure. Accordingly, other implementations are within the scope ofthe following claims.

What is claimed is:
 1. An apparatus comprising: a filter configured to(i) receive an input signal, and (ii) based on coefficients of apolynomial, filter the input signal to generate a first digital signal;a transmitter configured to transmit an analog signal according to again of the transmitter, wherein the analog signal is based on the firstdigital signal; a receiver configured to (i) receive the analog signaltransmitted by the transmitter, and (ii) output a second digital signalbased on the analog signal received by the receiver; a measurementmodule configured to, based on the second digital signal, generate alinearity signal indicative of a linearity of the transmitter; and again module configured to (i) receive the linearity signal, and (ii)control the gain of the transmitter according to the linearity signal,wherein the gain module is configured to set the gain of the transmitterto a predetermined value to maintain the coefficients of the polynomialwithin respective predetermined ranges.
 2. The apparatus of claim 1,wherein the linearity signal comprises at least one of: pre-distortioninformation including the coefficients of the polynomial; a magnitude ofan error vector of the analog signal received by the receiver; or aspectral mask of the analog signal received by the receiver.
 3. Theapparatus of claim 2, wherein: the magnitude of the error vector of theanalog signal is based on a difference between (i) constellation pointsof the first digital signal and (ii) predetermined constellation pointsof the transmitter; the measurement module comprises a detector; and thedetector is configured to determine the magnitude of the error vector ofthe analog signal.
 4. The apparatus of claim 2, wherein: the spectralmask is indicative of a spectrum of the analog signal; the measurementmodule comprises a spectral mask detector; and the spectral maskdetector is configured to determine the spectral mask.
 5. The apparatusof claim 1, wherein the gain module is configured to control the gain ofthe transmitter based on at least one of: a power level of the analogsignal received by the receiver; a voltage of a power supply of theapparatus; or a temperature of the apparatus.
 6. The apparatus of claim5, wherein: the measurement module comprises a power detector; and thepower detector is configured to measure the power level of the analogsignal received by the receiver.
 7. The apparatus of claim 5, wherein:the measurement module comprises a voltage detector; and the voltagedetector is configured to measure the voltage of the power supply. 8.The apparatus of claim 5, wherein: the measurement module comprises atemperature detector; and the temperature detector is configured tomeasure the temperature.
 9. The apparatus of claim 1, further comprisinga pre-distortion module configured to, based on the input signal andpre-distortion information, generate the first digital signal, wherein:the pre-distortion module is configured to, based on the pre-distortioninformation, pre-distort the first digital signal to compensate fordistortion caused by the transmitter; the linearity signal comprises thepre-distortion information; the measurement module includes a trainingmodule; the training module is configured to, based on the input signaland the second digital signal, provide the pre-distortion information;and the pre-distortion information includes the coefficients of thepolynomial.
 10. The apparatus of claim 9, further comprising a sourceconfigured to generate the input signal.
 11. The apparatus of claim 9,wherein the pre-distortion information is indicative of differencesbetween samples of the second digital signal and (ii) correspondingsamples of the input signal.
 12. A communication device comprising theapparatus of claim
 1. 13. The apparatus of claim 1, wherein: themeasurement module is configured to determine the coefficients of thepolynomial based on the second digital signal; and the linearity signalcomprises the coefficients of the polynomial.
 14. An apparatuscomprising: a transmitter configured to transmit a signal according to again setting, wherein the signal represents a first digital signal; areceiver configured to receive the signal transmitted by thetransmitter, and produce a second digital signal based on thetransmitted signal received by the receiver; a measurement moduleconfigured to produce a digital indication of a linearity of thetransmitter based on the second digital signal; a gain setting moduleconfigured to control the gain setting in accordance with the digitalindication of the linearity of the transmitter; and a digitalpre-distortion module configured to produce the first digital signalbased on a third digital signal and digital pre-distortion information,wherein the digital indication of the linearity of the transmittercomprises the digital pre-distortion information, the measurement moduleincludes a digital pre-distortion training module configured to producethe digital pre-distortion information based on the third digital signaland the second digital signal, the digital pre-distortion modulecomprises a digital filter, the digital filter is configured to producethe first digital signal based on the third digital signal and apolynomial, the digital pre-distortion information specifies values forcoefficients of the polynomial, and the gain setting module is furtherconfigured to set the gain setting to a maximum value that keeps thevalues of the coefficient within predetermined ranges.
 15. A methodcomprising: receiving an input signal; based on coefficients of apolynomial, filtering the input signal to generate a first digitalsignal; generating an analog signal based on the first digital signal;transmitting the analog signal from a transmitter and according to again of the transmitter; receiving the analog signal transmitted by thetransmitter; generating a second digital signal based on the receivedanalog signal; based on the second digital signal, generating alinearity signal indicative of a linearity of the transmitter, whereinthe linearity signal comprises the coefficients of the polynomial; andcontrolling the gain of the transmitter according to the linearitysignal.
 16. The method of claim 15, wherein the linearity signalcomprises at least one of: pre-distortion information including thecoefficients of the polynomial; a magnitude of an error vector of theanalog signal; or a spectral mask of the analog signal.
 17. The methodof claim 15, further comprising controlling the gain of the transmitterbased on at least one of: a power level of the analog signal; a voltageof a power supply of an apparatus comprising the transmitter; or atemperature of the apparatus.
 18. The method of claim 15, furthercomprising: based on the input signal and pre-distortion information,generating the first digital signal, wherein the linearity signalcomprises the pre-distortion information; and based on the input signaland the second digital signal, generating the pre-distortioninformation, wherein the pre-distortion information comprises thecoefficients of the polynomial.
 19. A method comprising: transmitting asignal, from a transmitter, according to a gain setting, wherein thesignal represents a first digital signal; receiving the transmittedsignal; producing a second digital signal based on the receivedtransmitted signal; producing a digital indication of a linearity of thetransmitter based on the second digital signal; controlling the gainsetting in accordance with the digital indication of the linearity ofthe transmitter; producing the first digital signal based on a thirddigital signal and digital pre-distortion information, wherein thedigital indication of the linearity of the transmitter comprises thedigital pre-distortion information; producing the digital pre-distortioninformation based on the third digital signal and the second digitalsignal; producing the first digital signal based on the third digitalsignal and a polynomial, wherein the digital pre-distortion informationspecifies values for coefficients of the polynomial; and setting thegain setting to a maximum value that keeps the values of the coefficientwithin predetermined ranges.
 20. The method of claim 18, wherein thepre-distortion information is indicative of differences between (i)samples of the second digital signal and (ii) corresponding samples ofthe input signal.
 21. The method of claim 15, further comprising settingthe gain of the transmitter to a maximum value to maintain thecoefficients of the polynomial within respective predetermined ranges.